Effect of the Retarder on Initial Hydration and Mechanical Properties of the"one-step"Alkaliactivated Composite Cementitious Materials

This paper studied the effects of different retarders on the performance of the"one-step"alkali-activated composite cementitious material(ACCM)which is composed of ground granulated blast slag(GGBS)and fly ash(FA),and analyzed its mechanical properties,hydration mechanism,and retardation mechanism.The effects of retarders on the hydration products,mechanical properties,and hydration kinetics of ACCM were investigated using XRD,SEM,FTIR,EDS,and thermoactive microcalorimetry.The results showed that Na_(2)B_(4)O_(7)·10H_(2)O(B)delayed the exotherm during the alkali activation process and could effectively delay the setting time of ACCM,but the mechanical properties were slightly decreased.The setting time of ACCM increased with the increase in SG content,but the mechanical properties of ACCM decreased with the increase in SG content.C1_(2)H_(22)O_(11)(CHO)could effectively delay the hydration reaction of ACCM and weakly enhanced the compressive strength.H_(3)PO_(4)(HP)at a concentration of 0.05 mol/L had a certain effect on ACCM retardation,but HP at a concentration of 0.07 and 0.09 mol/L had an effect of promoting the setting and hardening time of ACCM.

Exploring the potential of olivine-containing copper-nickel slag for carbon dioxide mineralization in cementitious materials

Water-quenched copper-nickel metallurgical slag enriched with olivine minerals exhibits promising potential for the production of CO_(2)-mineralized cementitious materials.In this work,copper-nickel slag-based cementitious material(CNCM)was synthesized by using different chemical activation methods to enhance its hydration reactivity and CO_(2) mineralization capacity.Different water curing ages and carbonation conditions were explored related to their carbonation and mechanical properties development.Meanwhile,thermogravimetry differential scanning calorimetry and X-ray diffraction methods were applied to evaluate the CO_(2) adsorption amount and carbonation products of CNCM.Microstructure development of carbonated CNCM blocks was examined by backscattered electron imaging(BSE)with energy-dispersive X-ray spectrometry.Results showed that among the studied samples,the CNCM sample that was subjected to water curing for 3 d exhibited the highest CO_(2) sequestration amount of 8.51wt%at 80℃and 72 h while presenting the compressive strength of 39.07 MPa.This result indicated that 1 t of this CNCM can sequester 85.1 kg of CO_(2) and exhibit high compressive strength.Although the addition of citric acid did not improve strength development,it was beneficial to increase the CO_(2) diffusion and adsorption amount under the same carbonation conditions from BSE results.This work provides guidance for synthesizing CO_(2)-mineralized cementitious materials using large amounts of metallurgical slags containing olivine minerals.

Effects of Water-cement Ratio and Hydration Heat Regulating Materials on Hydration Process of Early-age Cementitious Materials

By means of low-field nuclear magnetic resonance(LF-NMR),the transverse relaxation time(T_(2))signals of physically bound water in cement paste were monitored to indicate water content change and characterize the early-age hydration process.With the curves of the T_(2)signals and hydration time obtained,the hydration process could be divided into four typical periods using the null points of the second derivative curve,and the influences of water-cement ratio(w/c)and hydration heat regulating materials(HHRM)on hydration process were analyzed.The experimental results showed that the hydration rate of pure cement paste in accelerated period presented a positive correlation with w/c.Compared to pure cement paste,the addition of HHRM extended all four periods,and led to a much faster hydration rate in initial period as well as a slower rate in accelerated period.Finally,according to the LFNMR test results,the early-age hydration model of cementitious materials was proposed considering w/c and HHRM content.

Distribution of Na+and Mechanical Properties of Hardened Body of Alkali-activated Cementitious Materials

To explore the distribution of and the mechanical properties(compressive strength)of the hardened body of alkali slag-fly ash cementitious materials,this study was conducted by using the XRD,FTIR,SEM/EDS,and other test methods in three conditions:airtight drying(AD),airtight immersion(AI),and airtight soaking(AS).The 1D distribution law of free of hardened body under standard curing conditions was explored.The experimental results show that under standard curing conditions,the 1D distribution of within 0d-3 d shows a∨-shaped distribution,within 3-7 d show a∧-shaped distribution,and within 7-28 d tends to be balanced.The test results of leaching rate show that the free was the most stable under AD conditions and the hardened body bound the most by XRD,FTIR and SEM/EDS.And the compressive strength of the hardened body was the highest.The compressive strength of 28th reached 95.9 MPa.The definite distribution of provides an important reference for the strength development and durability evaluation of the hardened body of alkaliexcited cementitious materials.

Mechanical properties of gangue-containing aluminosilicate based cementitious materials

High performance aluminosilicate based cementitious materials were produced using calcined gangue as one of the major raw materials. The gangue was calcined at 500℃. The main constituent was calcined gangue, fly ash and slag, while alkali-silicate solutions were used as the diagenetic agent. The structure of gangue-containing aluminosilicate based cementitious materials was studied by the methods of IR, NMR and SEM. The results show that the mechanical properties are affected by the mass ratio between the gangue, slag and fly ash, the kind of activator and additional salt. For 28-day curing time, the compressive strength of the sample with a mass proportion of 2：1：1 （gangue： slag： fly ash） is 58.9 MPa, while the compressive strength of the sample containing 80wt% gangue can still be up to 52.3 MPa. The larger K^＋ favors the formation of large silicate oligomers with which AI（OH）4- prefers to bind. Therefore, in Na-K compounding activator solutions more oligomers exist which result in a stronger compressive strength of aluminosilicate-based cementitious materials than in the case of Na-containing activator. The reasons for this were found through IR and NMR analysis. Glauber＇s salt reduces the 3-day compressive strength of the paste, but increases its 7-day and 28-day compressive strengths.

Hydration kinetics of cementitious materials composed of red mud and coal gangue

To elucidate the intrinsic reaction mechanism of cementitious materials composed of red mud and coal gangue（RGC）, the hydration kinetics of these cementitious materials at 20°C was investigated on the basis of the Krstulovi？-Dabi？ model. An isothermal calorimeter was used to characterize the hydration heat evolution. The results show that the hydration of RGC is controlled by the processes of nucleation and crystal growth（NG）, interaction at phase boundaries（I）, and diffusion（D） in order, and the pozzolanic reactions of slag and compound-activated red mud-coal gangue are mainly controlled by the I process. Slag accelerates the clinker hydration during NG process, whereas the compound-activated red mud-coal gangue retards the hydration of RGC and the time required for I process increases with increasing dosage of red mud-coal gangue in RGC.

Effects of Steam Curing on the Resistance of Cementitious Materials to Chloride Penetration

The resistance to chloride penetration of cement-based material with different curing regimes was investigated by solution titration,XRD,LF-NMR and rapid chloride migration test.The results show that the curing regime has influences on the types and structure of the hydration products,which in turn affects their ability to bind chloride ions.The binding capacity of cementitious materials to chloride ions,porosity and chloride ion migration coefficient increased with the increase of water-cement ratio,while steam curing increased the porosity and chloride ion migration coefficient at the same time as it increased the chloride ion binding capacity of the materials.At lower water-cement ratios,the effect of steam curing on the resistance of cementitious materials to chloride ingress is negligible.

Effects of Technological Parameters on the Mechanical Performances of SAC-cementitious Materials

A new type of SAC-cementitious material was manufactured by taking sulphoaluminate cement(SAC) as the basic material, polyvinyl alcohol(PVA) as the organic polymer and adding coupling agent(KH). Its flexural strength can reach 165 MPa, the compressive strength can be larger than 267 MPa. A set of fitable technological parameters of the material were gained through experiments. In addition, the flexural strength and toughness can be improved greatly by adding KH, whose values can be increased by 49.76% and 14.55%, respectively.

Analysis of Hydration Mechanism and Microstructure of Composite Cementitious Materials for Filling Mining

To obtain the compositions and microstructure of hydration products of cementitious material in different hydration ages and its growth law of filling strength, the optimal proportion of composite cementitious material was determined according to the chemical composition of cement clinker which was composed of the Portland cement 32.5R, CSA 42.5 sulphoaluminate cement and two gypsum（CS）. The characterization of composite cementitious materials in different hydration ages was conducted by NMR, XRD and SEM techniques. The mechanism of hydration was explored. It is shown that the compressive strength of the test block increases gradually with the increase of hydration age. The microstructure of composite cementitious material can be changed from Al-O octahedron into Al-O tetrahedron in the hydration process. The hydrated alkali alumi niumsilicate formed with Si-O tetrahedron and Al-O tetrahedron. The degree of polymerization of Si-O tetrahedron gradually increased, and the structural strength of cementitious materials continued to increase. The diffraction peak of clinker minerals gradually decreased with the extension of hydration age. The CaSO4 completely hydrated to produce Aft during hydration which resulted in high early strength of cementitious material. The early hydration product of composite cementitious materials was Aft with a needle bar structure. The main middle and last hydration products were CSH gel and CH gel with dense prismatic shape. The microscopic pore of composite cementitious material gradually decreased and improved the later strength of filling block. The strong support was provided for mined-out area.

Optimization of SO_3 Content in Blended Cementitious Materials

Experimental investigation was conducted on the effects of gypsum types and SO 3 content on the fluidity and strengths of different cementitious systems.The experimental results show that influences of gypsum in various cementitious materials are different.For cementitious materials blended with various proportions of slag fly ash and 5% gypsum content,influences of gypsum and calcined gypsum on the fluidity and flexural/compressive strength are similar.It is revealed that 'combination effect' and 'synergistic effect' of slag and fly ash play an important role during hydration.For cementitious materials with 45% clinkers,30%slag,20%fly ash and 5%limestone,the optimized SO 3 contents in gypsum and calcined gypsum are 3.13% and 3.51% respectively and the optimized gypsum content is 6.5%.While both of them are blended,the optimum ratio of gypsum to calcined gypsum is 40%∶60%(total gypsum content 6.5%),correspondingly the optimum ratio of SO 3 is 19.3%∶32.4%.

Quantitative Determination of Composition of Quaternary Cementitious Materials

Based on the principle of ENV 196-4 ＂Methods of testing cement - Part 4 Quantitative determination of constituents or Chinese Standard GB/12960-2007 Quantitative measurement of mineral admixtures in cement, methods were developed for quantitative determination of fly ash, slag and limestone powder in fresh cement pastes, mortars and concretes. Limestone powder was determined using thermal analysis method. The residue content of fly ash on an 80um sieve, and silt contents of aggregate were also considered during the quantitative determination of mineral composition of quaternary cementitious system. With the developed methods, the deviations between the measured and the actual mineral contents of the constituent in the eemantitious material in fresh cement paste, mortar and concrete, were within 3%.

Preparation and Performance Study of Cementitious Capillary Crystalline Waterproof Materials

Cementitious capillary crystalline waterproof materials(CCCW for short)offer durability and excellent waterproofing properties,making them a popular option for building waterproofing.Some scholars have studied the proportioning of such materials.However,these studies lack the relationship between the impermeability pressure of mortar and the components,and the mechanism of action is somewhat debatable.Therefore,we adopted a two-step method in our experiments.Firstly,we screened out the components that significantly impact impermeability from a variety of active components by orthogonal test.We then optimized the design of the active group ratio using the simplex lattice method.Lastly,we conducted a performance test of the optimal ratio and explored the waterproofing mechanism of homemade CCCW.

Microscopic Analysis of Cementitious Sand and Gravel Damming Materia

The mechanical properties of cementitious sand and gravel damming material have been experimentally determined by means of microscopic SEM(Scanning Electron Microscopy)image analysis.The results show that the combination of fly ash and water can fill the voids in cemented sand and gravel test blocks because of the presence of hydrated calcium silicate and other substances;thereby,the compactness and mechanical properties of these materials can be greatly improved.For every 10 kg/m^(3) increase in the amount of cementitious material,the density increases by about 2%,and the water content decreases by 0.2%.The amount of cementitious material used in the sand and gravel in these tests was 80-110 kg/m^(3),the water-binder ratio was 1-1.50.Moreover,the splitting tensile strength was 1/10 of the compressive strength,and the maximum strength was 7.42 MPa at 90 d.The optimal mix ratio has been found to be 50 kg of cement,60 kg of fly ash and 120 kg of water(C50F60W120).The related dry density was 2.6 g/cm^(3),the water content was 6%,and the water-binder ratio was 1.09.

Influence on Microstructure of Micronized Sand as Cement Replacement in Cementitious Materials

In this study,micronized sand is selected as a kind of filler to partially replace cement in cementitious materials. This filler is considered as chemically inert material,which can not react with water or hydration products,but still indirectly influences the hydration in a positive way. In the experimental program,non-evaporable water test was carried out to determine the degree of hydration of cement paste with and without micronized sands. The influence of different finenesses of sand particles,240 m2/kg,400 m2/kg and 1 300 m2/kg,and different curing ages were investigated. The SEM image analysis was used to characterize the morphological changes of microstructure by the presence of the micronized sand during the cement hydration process. Hydration reaction is enhanced by the use of inert micronized sands. The fineness of micronized sands influences the degree of hydration a lot. The fineness factor has been taken into account in the simulation. There is a clear interface area between sand particle and hydration products.

Preparation and Microstructure Analysis of High Strength Cementitious Materials Containing Metakaolin

The preparation and microstructure analysis of high strength cementitious materials containing metakaolin (MK) was studied in this paper. The MK was prepared firstly,and then was mixed with fly ash,ground blast furnace slag,quartz powder and cement with different percentage to produce high strength cementitious materials. After cured under different environment,the compressive strength of such materials was tested. Techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM) were further employed to identify the composition and microstructure. The results obtained reveal that the compressive strength of such materials mainly effected by component of raw materials,the water binder ratio (W/B) and the curing regime. When the three factors above are optimized,the compressive strength of such materials can get to 156 MPa in maximum. The X-ray diffraction analysis and the scanning electron microscopic images indicated that under optimal curing condition,more raw materials can take chemical reaction and the microstructure is dense to yield good mechanical properties.

The Effect of Wet-grinding on the Properties of Glass Powder and Its Application in Cement Based Materials

To improve the pozzolanic reactivity,waste glass(WG)needs to be micronized to fine particles so as to expedite the leaching of active constituent.The key feature of this work is to examine the effect of wet-grinded WG on the mechanical and structural properties of cement based materials.The experimental results show that wet-grinding can improve the ions leaching behavior of WGP and decrease the stability of silicon oxide bond.The pozzolanic reactivity of WGP was dramatically enhanced after wet-grinding,as high as 144.1%at 1 d and 110.9%at 28 d when the mean grain size of WGP reached 0.90μm.The ground WGP can promote the transformation of capillary pores to gel pores to improve the compactness of microstructure regardless of the reaction time.

The NMR core analyzing tomograph:a multi-functional tool for non-destructive testing of building materials

NMR is becoming increasingly popular for the investigation of building materials as it is a non-invasive technology that does not require any sample preparation nor causes damage to the material.Depending on the specific application it can offer insights into properties like porosity and spatial saturation degree as well as pore structure.Moreover it enables the determination of moisture transport properties and the(re-)distribution of internal moisture into different reservoirs or chemical phases upon damage and curing.However,as yet most investigations were carried out using devices originally either designed for geophysical applications or the analysis of rather homogeneous small scale(<10 mL)samples.This paper describes the capabilities of an NMR tomograph,which has been specifically optimized for the investigation of larger,heterogeneous building material samples(diameters of up to 72 mm,length of up to 700 mm)with a high flexibility due to interchangeable coils allowing for a high SNR and short echo times(50-80 ms).

Enhanced photocatalytic performance of cementitious material with TiO_2@Ag modified fly ash micro-aggregates

A TiO2 photocatalyst is coated on the surface of a zeolite fly ash bead（ZFAB） to improve its dispersability and exposure degree in a cement system.The application of Ag particles in TiO2/ZFAB modified cementitious materials is to further enhance the photocatalytic performance.Various Ag@TiO2/ZFAB modified cementitious specimens with different Ag dosages are prepared and the characteristics and photocatalytic performance of the prepared samples are investigated.It is observed that the multi-level pore structure of ZFAB can improve the exposure degree of TiO2 in a cement system and is also useful to enhance the photocatalytic efficiency.With an increment of the amounts of Ag particles in the TiO2/ZFAB modified cementitious samples,the photocatalytic activities increased first and then decreased.The optimal Ag@TiO2/ZFAB modified cementitious sample reveals the maximum reaction rate constant for degrading benzene（9.91×10^-3 min^-1）,which is approximately 3 and 10 times higher than those of TiO2/ZFAB and TiO2 modified samples,respectively.This suggests that suitable Ag particles coupled with a ZFAB carrier could effectively enhance the photocatalytic effects and use of TiO2 in a cement system.Thus,ZFAB as a carrier could provide a potential method for a high efficiency engineering application of TiO2 in the construction field.

Iron ore tailings used for the preparation of cementitious material by compound thermal activation

In the background of little reuse and large stockpile for iron ore tailings, iron ore tailing from Chinese Tonghua were used as raw material to prepare cementitious materials. Cementitious properties of the iron ore tailings activated by compound thermal activation were studied. Testing methods, such as XRD, TG-DTA, and IR were used for researching the phase and structure variety of the iron ore railings in the process of compound thermal activation. The results reveal that a new cementitious material that contains 30wt% of the iron ore tailings can be obtained by compounded thermal activation, whose mortar strength can come up to the standard of 42.5 cement of China.

The pH of Cement-based Materials:A Review

Cement-based materials (CBMs),such as paste,mortar and concrete,are highly alkaline with an initial high pH of approximately 12.0 to 13.8.CBMs have a high pH due to the existing oxide mineral portlandite and alkali metal contents in Portland cement.The high pH of concrete provides excellent protection and reinforces the steel bars against corrosion.The pH of concrete does not remain constant due to ageing and other defect-causing factors,such as chloride ingress,alkali leaching,carbonation,corrosion,acid attack,moisture and biodegradation process.Reducing the concrete pH has negative impact on the strength,durability and service life of concrete buildings.However,the high pH of concrete may also cause concrete structure deterioration,such as alkali silica reaction,porosity and moisture related damages in concrete structures.The pH of CBMs can be influenced by high temperatures.For instance,the extremely high volume (85%-100%) of slag-blended cement pastes shows considerable pH reduction from 12.80 to 11.34 at 800 ℃.As many concrete structure deterioration are related to concrete pH,using an accurate and reliable method to measure pH and analyse the durability of reinforced concrete structure based on pH values is extremely important.This study is a comprehensive review of the pH of CBM in terms of measurement,limitations and varying values for different CBM types.